There has been known an exhaust gas treatment apparatus that removes mercury from exhaust gas using a denitration apparatus and a wet desulfurization apparatus. At this time, the denitration apparatus reduces nitrogen oxide NOx contained in the exhaust gas to nitrogen, and oxidizes elemental mercury contained in the exhaust gas to water-soluble mercury using hydrogen chloride HCl contained in the exhaust gas. The wet desulfurization apparatus desulfurizes the denitrated exhaust gas, and removes the oxidized mercury from the denitrated exhaust gas (refer to PTLs 1, 2, and 3).
In such exhaust gas treatment apparatus, since desulfurization drainage that the wet desulfurization apparatus drains contains chlorine, desulfurization drainage is further supplied to fuel for a boiler or inside a furnace of the boiler, thereby a supply amount, which is the amount of chlorine supplied from the outside of a system, the chlorine oxidizing elemental mercury, can be reduced, and a discharge amount, which is the amount of the desulfurization drainage discharged to the system, can be reduced.
In PTL 4, an exhaust gas treatment system is disclosed in which desulfurization drainage is directly sprayed into a path to supply fuel to a boiler and a furnace of the boiler.
In PTL 5, a wet flue-gas desulfurization apparatus is disclosed in which a percentage of moisture content in gypsum collected from an absorbing liquid is adjusted according to an amount of chlorine absorbed in the absorbing liquid that is previously calculated depending on a load of a combustion apparatus, a type of fuel to be used, and a property of exhaust gas, and thereby a chlorine concentration in the absorbing liquid is suppressed to not more than a predetermined value.
In PTL 6, a flue-gas desulfurization apparatus is disclosed in which filtrate obtained by separating gypsum from gypsum slurry generated from an absorbing liquid joins the absorbing liquid.
In PTL 7, a wet flue-gas desulfurization apparatus is disclosed in which a supernatant liquid of slurry is electrolyzed into chlorine gas or hydrogen chloride gas, a chlorine concentration of the slurry is adjusted to a predetermined concentration, and the slurry is circulated through an absorption tower.